Gas port sealing for CVD/CVI furnace hearth plates

ABSTRACT

A method and apparatus for sealing gas ports in CVD/CVI furnaces and processes is disclosed. A fluid direction nozzle ( 160 ) is positioned between a top lip ( 101 ) of a gas inlet port ( 100 ) delivering a reactant gas (G) to a furnace compartment( 200 ) in a CVD/CVI furnace ( 10 ) and corresponding holes ( 151 ) of a CVD/CVI process apparatus such as a hearth plate ( 150 ). The fluid direction nozzle  160  reduces leakage of reactant gases (G) and ensures a smooth transition of gas flow direction between the gas inlet port ( 100 ) and the corresponding holes ( 151 ). CVD/CVI process times are significantly reduced with the use of the reusable/replaceable flow direction nozzles ( 160 ).

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

[0001] This application is a divisional of co-pending U.S. applicationSer. No. 09/874,653 filed Jun. 5, 2001 the entire contents of which areherein incorporated by reference.

[0002] The present invention is generally directed to Chemical VaporDeposition/Infiltration (CVD/CVI) apparatus and processes, and moreparticularly to a method and apparatus utilizing a flow direction nozzlein a CVD/CVI furnace for improving CVD/CVI process time and reducing gasleakage.

BACKGROUND OF THE INVENTION

[0003] Chemical vapor deposition and infiltration (CVD/CVI) is awell-known process for depositing a binding matrix within a porousstructure. The term “chemical vapor deposition” (CVD) generally impliesdeposition of a surface coating, but the term is also used to refer toinfiltration and deposition of a matrix within a porous structure. Theterm CVD/CVI is intended to refer to infiltration and deposition of amatrix within a porous structure.

[0004] CVD/CVI is particularly suitable for fabricating high temperaturestructural composites by depositing a carbonaceous or ceramic matrixwithin a carbonaceous or ceramic porous structure resulting in veryuseful structures such as carbon/carbon aircraft brake disks, andceramic combustor or turbine components. The generally known CVD/CVIprocesses may be classified into four general categories: isothermal,thermal gradient, pressure gradient, and pulsed flow. The specificprocess times and steps, reactant gas and CVD/CVI furnaces andassociated apparatus may vary depending on which of these four generalcategories is utilized.

[0005] U.S. Pat. No. 6,162,298 and corresponding European PatentApplication EP 0 997 553 A1 to Rudolph describe these and other CVD/CVIprocesses and apparatus in further detail. Rudolph particularlydescribes a sealed reactant gas inlet for a CVD/CVI furnace.

[0006]FIG. 1 is a side cross-sectional view of a furnace according toU.S. Pat. No. 6,162,298. A generally cylindrical furnace 10 configuredto be employed with a high temperature process is shown. The furnaceincludes a steel shell 12 and a steel lid 14. The shell 12 includes aflange 16 and the lid 14 includes a mating flange 18 that seals againstflange 16 when the lid 14 is installed upon the shell 12, as shown inFIG. 1. The lid also includes a vacuum port 20.

[0007] The shell 12 and lid 14 together define a furnace volume 22 thatis reduced to vacuum pressure by a steam vacuum generator (not shown) influid communication with the vacuum port 20. The shell 12 rests upon amultitude of legs 62. The furnace 10 also includes a cylindricalinduction coil 24 adjacent a cylindrical susceptor 26. The inductioncoil 24 includes coiled conductors 23 encapsulated by electricalinsulation 27.

[0008] During operation, the induction coil 24 develops anelectromagnetic field that couples with the susceptor 26 and generatesheat within the susceptor 26. The induction coil 24 may be cooled,typically by integral water passages 25 within the coil 24. Thesusceptor 26 rests upon a susceptor floor 28 and is covered by asusceptor lid 30. A cylindrical insulation wall 32 is disposed inbetween the susceptor 26 and the induction coil 24. A lid insulationlayer 34 and a floor insulation layer 36 are disposed over the susceptorlid 30 and beneath the susceptor floor 28, respectively.

[0009] The susceptor floor 28 rests upon the insulation layer 36, which,in turn, rests upon a furnace floor 38. The furnace floor 38 is attachedto the shell 12 by a floor support structure 40 that includes amultitude of vertical web structures 42.

[0010] A reactant gas is supplied to the furnace 10 by a main gas supplyline 44. A plurality of individual gas supply lines 46 are connected influid communication with a plurality of gas ports 48 that pass throughthe furnace shell 12. A plurality of flexible gas supply lines 50 areconnected in fluid communication with the gas ports 48 and a multitudeof gas inlets 52 that pass through holes 54 in the furnace floor 38, thefloor insulation layer 36, and the susceptor floor 28.

[0011] U.S. Pat. No. 6,162,298 further describes a gas preheater 56resting on the susceptor floor 28 and including a multitude of stackedperforated plates 58 that are spaced from other by a spacing structure60. Each plate 58 is provided with an array of perforations that arehorizontally shifted from the array of perforations of the adjacentplate 58. This causes the reactant gas to pass back and forth throughthe plates, which diffuses the reactant gas within the preheater 56 andincreases convective heat transfer to the gas from the perforated plates58. A multitude of porous substrates 62, for example brake disks, arestacked within the furnace 10 inside the susceptor 26 on fixtures (notshown).

[0012] Further, U.S. Pat. No. 6,162,298 is directed toward preventinggas leakage around the gas inlet 52 extending through the hole 54 in thesusceptor floor 28 in the CVD/CVI furnace 10. The method and apparatusseal the gas inlet 52 to the susceptor floor 28 with sufficient intimacyto block leakage of gas through the hole 54 around the gas inlet 52while allowing the gas inlet 52 to cyclically translate through the hole54, as indicated by arrow 55, due to thermal expansion and contractioninduced by thermal cycles in the CVD/CVI furnace 10.

[0013] Reactant gas entry through the gas inlets 52 is diffused withinthe preheater 56 and eventually reaches the porous substrates 62.However, reactant gas leaving the gas inlets 52 follows a tortuous pathas it travels back and forth through the plates 58.

SUMMARY OF THE PRESENT INVENTION

[0014] The present invention overcomes the shortcomings associated withthe background art and achieves other advantages not realized by thebackground art.

[0015] The present invention, in part, is a recognition that currentCVD/CVI process time is lengthy and results in considerable expense. Thepresent invention provides a CVD/CVI method and apparatus that reducesprocess time, ensures efficient use of reactant gases, and permits anincrease in process output.

[0016] The present invention, in part, is a recognition that reactantgas, such as densification gas, delivered directly to target carbonparts, will greatly improve process time.

[0017] The present invention, in part, provides a gas inlet portassembly for a CVD/CVI furnace having a furnace compartment and aCVD/CVI process apparatus with a plurality of holes, the gas inlet portassembly comprising a plurality of gas inlet ports delivering processgas to the furnace compartment; and a plurality of flow directionnozzles positioned between the holes of the CVD/CVI process apparatusand the gas inlet ports.

[0018] The present invention, also in part, provides a flow directionnozzle assembly for a CVD/CVI furnace, the flow direction nozzleassembly comprising a flow direction nozzle including a gas inlet portsealing portion; a support shoulder; and a nozzle portion.

[0019] The present invention, also in part, provides a method forsealing gas inlet ports for delivering a process gas in a CVD/CVIfurnace, the method comprising positioning flow direction nozzles alongupper lips of the gas inlet ports; loading a CVD/CVI process apparatushaving a plurality of gas inlet holes into the furnace; sealinglyengaging the flow direction nozzles to the gas inlet holes of theprocess apparatus to create a gas path-directing, fluid seal.

[0020] Advantages of the present invention will become more apparentfrom the detailed description given hereinafter. However, it should beunderstood that the detailed description and specific examples, whileindicating preferred embodiments of the present invention, are given byway of illustration only, since various changes and modifications withinthe spirit and scope of the present invention will become apparent tothose skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus do not limit thepresent invention.

[0022]FIG. 1 is a side cross-sectional view of a furnace according tothe background art;

[0023]FIG. 2 is a side cross-sectional view of a furnace incorporatingan embodiment of the present invention;

[0024]FIG. 3 is an enlarged, side cross-sectional view of hearth plateand flow direction nozzle assemblies according to an embodiment of thepresent invention;

[0025]FIG. 4 is an enlarged, side cross-sectional view of a flowdirection nozzle assembly and gas inlet port according to an embodimentof the present invention; and

[0026]FIG. 5 is a side, partial cross sectional view of a flow directionnozzle according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The present invention will now be described in detail withreference to the accompanying drawings.

[0028]FIG. 2 is a side cross-sectional view of a furnace incorporatingan embodiment of the present invention. FIG. 3 is an enlarged, sidecross-sectional view of hearth plate and flow direction nozzleassemblies according to an embodiment of the present invention. FIG. 4is an enlarged, side cross-sectional view of a flow direction nozzleassembly and gas inlet port according to an embodiment of the presentinvention. FIG. 5 is a side, partial cross sectional view of a flowdirection nozzle according to an embodiment of the present invention.

[0029]FIG. 2 is a side cross-sectional view of an exemplary furnaceincorporating an embodiment of the present invention. One of skill inthe art will appreciate that the actual furnace construction and CVD/CVIprocesses implemented will vary according to the products undergoingtreatment within the furnace compartment 200. Accordingly, the CVD/CVIfurnace 10 shown in FIG. 2 simply indicates one type of application ofthe present invention.

[0030] A generally cylindrical furnace 10 configured to be employed in adensification process for carbon fiber based brakes is shown in FIG. 2.The furnace includes a steel shell 12 and a steel lid 14. The shell 12includes a flange 16 and the lid 14 includes a mating flange 18 thatseals against flange 16 when the lid 14 is installed upon the shell 12,as shown in FIG. 1. The lid may also include a vacuum port 20.

[0031] The shell 12 and lid 14 together define a furnace volume 22 thatmay be reduced to vacuum pressure by a steam vacuum generator (notshown) in fluid communication with the vacuum port 20. The shell 12rests upon a multitude of legs 62. The furnace 10 may also be providedwith a cylindrical induction coil 24 adjacent a cylindrical susceptor26. The induction coil 24 includes coiled conductors 23 encapsulated byelectrical insulation 27. However, induction cooling is not necessary ina preferred embodiment of the present invention.

[0032] During operation, the induction coil 24 develops anelectromagnetic field that couples with the susceptor 26 and generatesheat within the susceptor 26. The induction coil 24 may be cooled,typically by integral water passages 25 within the coil 24. Thesusceptor 26 rests upon a susceptor floor 28 and is covered by asusceptor lid 30.

[0033] A cylindrical insulation wall 32 is disposed in between thesusceptor 26 and the induction coil 24. A lid insulation layer 34 and afloor insulation layer 36 are disposed over the susceptor lid 30 andbeneath the susceptor floor 28, respectively. The susceptor floor 28rests upon the insulation layer 36, which, in turn, rests upon a furnacefloor 38. The furnace floor 38 is attached to the shell 12 by a floorsupport structure 40 that includes a multitude of vertical webstructures 42.

[0034] As seen in FIG. 2, a reactant gas G is supplied to the furnace 10by a main gas supply line 44. A plurality of individual gas supply lines46 are connected in fluid communication with a plurality of gas ports 48that pass through the furnace shell 12. A plurality of flexible gassupply lines 50 are connected in fluid communication with the gas ports48 and a multitude of gas inlet ports 100 that pass through holes 54 inthe furnace floor 38, the floor insulation layer 36, and the susceptorfloor 28.

[0035] When the aforementioned CVD/CVI furnace 10 is used for densifyingfiber-based brakes, the carbon parts are first stacked on a hearth plate150. The hearth plate 150 is then loaded into the furnace 10. The gas Gthat is intended to densify the carbon parts enters the furnacecompartment 200 through the gas inlet ports 100.

[0036] Prior to the present invention, the reactant gas G wouldeventually travel through holes formed in the bottom of the hearth plate150, or whatever mating apparatus is otherwise loaded within the furnacecompartment 200. However, the CVD/CVI processes, particularly CVDprocesses, are often time-consuming processes. Accordingly, it isimportant that all of the gas G that is fed to the furnace compartment200 reaches the parts for densification directly.

[0037]FIG. 3 is an enlarged, side cross-sectional view of hearth plateand flow direction nozzle assemblies according to an embodiment of thepresent invention. As seen in FIG. 3, a hearth plate 150 having aplurality of holes 151 is arranged above the furnace floor 38 and gasinlet ports 100.

[0038] The gas G exiting the gas inlet ports 100 would eventually flowto the adjacent holes 151 of the hearth plate in conventionalapplications of the background art. However, the present inventors havefound that this lack of complete sealing between gas inlet port top lips101 and the hearth plate bottom holes 151 in these conventionalapplications can be prevented by the present invention.

[0039] Accordingly, a plurality of flow direction nozzles 160 areemployed in positions between the gas inlet port top lips 101 and thehearth plate holes 151. These flow direction nozzles 160 perform both asealing function and a fluid directing function. The flow directionnozzles 160 produce a direct flow alignment between the gas inlet port100 and the corresponding inlet holes 151 of the mating apparatus.

[0040] The flow direction nozzles 160 prevent the gas G from leaking andbecoming misdirected away from the corresponding holes 151 of the hearthplate 150 (or other apparatus placed within the furnace compartment200). The flow direction nozzles 160 thereby improve process times and asmooth transition of gas direction from the gas inlet ports 100 to thehearth plate/apparatus holes 151. Accordingly, all of theprocess/reactant gas G is directed toward the holes 151 of the hearthplate 150 and the carbon parts positioned thereon.

[0041]FIG. 4 is an enlarged, side cross-sectional view of a flowdirection nozzle assembly and gas inlet port according to an embodimentof the present invention. FIG. 4 shows a single hearth plate hole 151sealingly engaged with a gas inlet port upper lip 101 of a correspondinggas inlet port 100. A flow direction nozzle 160 is provided between thegas inlet port 100 and the hearth plate hole 150.

[0042] A GRAFOIL® brand of sealing disc 130 is provided between the flowdirection nozzle 160 and the hearth plate 150 (or other matingapparatus) on an outlet side of the flow direction nozzle 160. A ceramicprotection tube material 110, such as a mullite tube, may be providedalong an interior of the gas inlet port 100, the interior defined by theregion located within the internal diameter 107 of the gas inlet port100. An additional GRAFOIL® sealing disc 120 may be incorporated betweenan upper edge of the ceramic protection tube material 110 and theinternal diameter 107 of the gas inlet port 100 on an inlet side of theflow direction nozzle 160.

[0043] In a preferred embodiment, the flow direction nozzles 160 areessentially annular shaped collars that can molded, cast or machined.Although one of skill in the art will appreciate that there are severalsuitable materials for the flow direction nozzles 160 and thepotentially high temperature, pressure and severe operating environmentof CVD/CVI processes, a preferred embodiment includes nozzles 160constructed of graphite. One of skill in the art will further appreciatethat graphite includes and is not limited to molded graphite,crystalline graphite, recrystallized graphite, graphite fiber-reinforcedgraphite composites and graphite-graphite composites.

[0044] As aforementioned, GRAFOIL® brand of flexible graphite, isdesirable for its superior sealing ability particular with respect tofluids/gases, ability to withstand severe temperature and pressureenvironments, corrosion resistance, easy removal and installation, andresiliency. The Grafoil® sealing discs 120, 130 are used to compensatefor dimensional distortion between the apparatus' bottom surface, e.g.hearth plate 150 and the flow direction nozzle 160. In an exemplaryembodiment, the sealing discs 120, 130 are annular sealing discs orrings.

[0045] Further, mullite, utilized in a tube 110 of an embodiment of thepresent invention, is particularly advantageous due to its common use asa refractory material for firebrick and furnace linings, flameresistance, low, uniform coefficient of thermal expansion, and heatconductivity. However, one of skill in the art will appreciate thatalternative materials can be incorporated into the present invention,particularly those showing common properties with those specificallylisted in the foregoing embodiments.

[0046]FIG. 5 is a side, partial cross sectional view of a flow directionnozzle according to an embodiment of the present invention. As seen inFIG. 4 and FIG. 5, the annular flow direction nozzle 160 is designed tofit into the gas inlet port 100. The flow direction nozzle 160 includesa gas inlet port sealing portion 161 matingly engaging the correspondinginternal diameter 107 of the gas inlet port 100 and defining an inletregion of the flow direction nozzle 160. The gas inlet port sealingportion 161 ensures admission of gas G into an interior of the flowdirection nozzle 160. The flow direction nozzle also include a machinedsupport shoulder 163 resting on the gas inlet port top lip 101. Themachined support shoulder 163 designed to support a corresponding lowersurface of an apparatus being loaded above the gas inlet ports 100, suchas the hearth plate 150. A nozzle portion 162 of the flow directionnozzle 160 extends into the apparatus being loaded, e.g. hearth platehole 151.

[0047] As seen in FIG. 4 and FIG. 5, the flow direction nozzle 160 andhearth plate holes 151 can also be provided with chamfered surfaces. Achamfered surface 165 of the flow direction nozzle 160 additionallyprovides smooth, fluid flow. The hearth plate 150 or other apparatusbeing loaded into the furnace compartment 200 is supported by the flowdirection nozzles 160.

[0048] In an exemplary embodiment, the gas inlet ports 100 can be cut toa length of approximately 3.5 inches. A gas inlet port outer diameter106 can be approximately 1 inch larger, e.g. have a tube thickness 105of 1 inch. As seen in FIG. 5, the flow direction nozzle 160 may havevertical dimensions of approximately a=1.50 to 2.00 inches, b=0.50inches, and c=0.50 inches. Approximate horizontal dimensions of the flowdirection nozzle 160 may include d=0.50 inches, e=0.00 to 0.75 inches,and f=1.25 inches. However, one of ordinary skill in the art willappreciate that these values will be routinely modified to suit theparticular size of mating components such as varying gas inlet port sizeand varying hearth plate hole diameters. Further, although relativesizes have been depicted in the accompanying drawings, one of skill inthe art will appreciate that FIG. 1 through FIG. 5 are not necessarilydrawn to scale.

[0049] A method according to the present invention will now be describedwith reference to the accompanying drawings and foregoing description ofFIGS. 2-5. The present invention is directed toward a method ofproviding a fluid seal between a gas inlet port and a CVD/CVI processapparatus, such as a hearth plate 150. The method includes positioningflow direction nozzles 160 along each gas inlet port top lip 101 of aplurality of gas inlet ports 100.

[0050] A CVD/CVI process apparatus to be loaded within a furnacecompartment 200, such as a hearth plate 150, is then positioned abovethe flow direction nozzles 160. Corresponding process apparatus holes,such as hearth plate holes 151, are sealingly engaged with the flowdirection nozzles 160 to create a fluid/gas seal. Accordingly, reactantgas G is prevented from being misdirected away from correspondingprocess apparatus holes and from leaking away from the targeted, CVD/CVIprocess apparatus. The flow direction nozzles 160 can be reused andeasily replaced as they become worn, damaged or lost.

[0051] Further examples of suitable materials, CVD/CVI process steps andapparatus, and potential applications of the present invention aredescribed in U.S. Pat. No. 6,162,298 to Rudolph; the entirety of whichis hereby incorporated by reference. Further, one of skill in the artwill appreciate that the specific furnace and fixture configurationslisted in the foregoing description are merely exemplary of some of themany applications of the present invention.

[0052] Accordingly, the type of CVD/CVI processes and furnaces employedmay vary substantially depending upon the targeted products, e.g.aircraft brakes, internal combustion engine components, gas or steamturbine parts, etc.. As such, the furnace configuration of FIG. 2 ispresented by way of example, and is not intended to limit the inventionto the specific arrangement presented. Further, although an annular flowdirection nozzle 160 has been described, one of skill in the art willappreciate that the geometry of the flow direction nozzle can be variedto effect changes in pressure, flow path, and/or gas velocity,particularly with respect to well known characteristics of affectingnozzle/venturi flow paths.

What is claimed is:
 1. A method for sealing gas inlet ports fordelivering a process gas in a CVD/CVI furnace, said method comprising:positioning flow direction nozzles along upper lips of said gas inletports; loading a CVD/CVI process apparatus having a plurality of gasinlet holes into said furnace; sealingly engaging the flow directionnozzles to said gas inlet holes of said process apparatus to create agas-path directing, fluid seal.
 2. The method according to claim 1,wherein the CVD/CVI process apparatus is a hearth plate having hearthplate holes, and the CVD/CVI process is a densification process forcarbon fiber based brakes.
 3. The method according to claim 1, furthercomprising the step of: replacing the flow direction nozzles withreplacement flow direction nozzles as the flow direction nozzles becomedamaged or worn.
 4. The method according to claim 1, wherein the flowdirection nozzles are annular shaped collars made of graphite.